The invention concerns an optical transmitting and receiving device for the contact-free reading of marks and more particularly includes transmitter and receiver diodes positively positioned with their axial beams constricted by slots and intersecting at a reference surface for high resolution reading.
Transmitting and receiving devices of this type are known from U.S. Pat. No. 4,079,261 and, in essence from IBM Technical Disclosures Bulletin Vol. 14, No. 1, June 1971, Pages 58, 59.
A disadvantage in these referenced structures is that the size of the rectangular cutout is still in the area of the dimension of the housing of the transmitter and/or receiver diode. This, combined with technical production inaccuracies in the edge area of the optical piece parts, which are mostly mass produced can lead to dispersion on the reference surface or to transition-time distortion on the receiver diode, both of which limit the accuracy and reliability of operation. Further, beam reflections can form disadvantageously on the inner face of the cutouts through which the beams pass which can impair the reading procedure with reference to the reading speed and resolution in the case of small markings. It is also disadvantageous that those cutouts, in the case of the known device, on the upper face of the plastic body, form differently-sized openings when compared with each other. Thus contamination can have a detrimental one-sided impairment of the beam path which with reference to the reading procedure causes slow-acting impairment which is often noticed too late.
From French Pat. No. 25 55 337 the insertion of a frame with an optical slotted diaphram in the beam path of the transmitter and receiver diode is known. This is however disadvantageous in that reflections form on the side of the frame nearest to the optical parts, which can impair the accuracy of the reading. Furthermore, there exists the danger that the frame with the slotted diaphram could slide into the beam path.